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California Incident Summary
Equine Contagious Metritis
Disease Background
Contagious Equine Metritis (CEM) is a highly contagious
venereal Foreign Animal Disease of horses caused by the
bacteria Taylorella equigenitalis. The disease is not
known to affect humans or other species of livestock.
Disease transmission occurs during breeding by natural
cover or artificial insemination.
Most CEM cases involve non-clinical mares with mild
uterine inflammation. Asymptomatic mares can be
infectious and remain carriers for several months. An
acute infection can cause active inflammation of the
endometrium that results in a mucoid, vulvar discharge
10-14 days post-breeding. Abortions due to CEM are
rare. Mares infected during pregnancy can produce
subclinical carrier foals. Infected stallions exhibit no
clinical signs but can carry the organism on their external
genitalia for an extended period of time.
Carrier mares and stallions act as a reservoir of T.
equigenitalis. Undiagnosed mares and stallions are the
source of infection in disease outbreaks. Detection of the
carrier state relies on isolation of the bacteria from
urogenital swabs. Due to the fastidious nature and slow
growth characteristics of the organism, it is difficult to
culture and thus, requires obtaining multiple culture
samples over a period of one week.
Testing and Treatment Protocols
Exposed stallion testing protocols include two sets of
cultures and breeding of two qualified negative test
mares. The test mares are cultured on days 3, 6, 9 and
28 post breeding and bled for compliment fixation
testing on day 21 post breeding. Stallions are released
from quarantine with negative pre-breeding cultures,
negative test mare cultures and negative test mare
compliment fixation test.
Since stallions do not develop detectable antibodies, the
serologic test is only useful in the detection of CEM
antibodies in mares. Successful treatment of CEM
culture-positive mares and stallions is through the use
of appropriate antibiotics.
T. equigenitalis infections of carrier horses may be
eliminated by washing the external genitalia with
disinfectants and treating with a local antibiotic. The
organism may be more readily eliminated from stallions
and treatment of the mare can take up to several weeks
and may include systemic antibiotic treatment.
Prevention
Currently, the United States (U.S.) is considered free of
Contagious Equine Metritis. To ensure this free status,
it is required that horses over two years of age being
imported from CEM affected countries are quarantined
and screened for T. equigenitalis.
In countries where the disease is present, it is
controlled by only breeding stallions and mares which
are CEM test negative and are not known to be CEM
carriers. Critical disease control measures are excellent
hygiene during reproductive procedures and cleaning
and disinfection of potential fomites, such as breeding
equipment and breeding mounts.
Continued on next page
May 2016
Animal Health and Food Safety Services Animal Health Branch
Headquarters - (916) 900-5002 Redding District - (530) 225-2140 Modesto District - (209) 491-9350
Tulare District - (559) 685-3500 Ontario District - (909) 947-4462
USDA-APHIS-VS - (916) 854-3950 or (877) 741-3690
For more information, please click the following: Animal Health Branch
CDFA Equine Health Information and Resources Hand Washing Why, When, How, and with What?
California Incident Summary
Contagious Equine Metritis— Page 2 of 2
2013 California CEM Incident
In January 2013, a private practitioner working up a 17
year old Lusitano mare for history of infertility, submitted
samples to the California Animal Health and Food Safety
Laboratory (CAHFS) for culture. The CAHFS Laboratory
cultured the sample and based on suspicious growth,
subsequently sent it to the National Veterinary Services
Laboratory (NVSL), where it was confirmed positive for
Taylorella equigenitalis, the organism responsible for
CEM. This mare is considered the index case for the 2013
CEM outbreak. The California Department of Food and
Agriculture, Animal Health Branch (AHB) conducted an
intense epidemiological investigation leading to the
detection of three additional confirmed CEM positive cases
and twenty-two exposed horses.
The first positive stallion identified was a 20 year old
Lusitano Stallion, imported from Brazil in 2003, who was
bred to the index mare by live cover and artificial
insemination. During the 2012 breeding season, the
positive Lusitano stallion was collected at a stallion station
in California, prompting the AHB to identify and test all
exposed stallions1 and mares2. In addition to the index
mare and Lusitano stallion, one exposed stallion (a
domestic 25 year old Lipizzaner stallion that had semen
collected at the same facility as the positive Lusitano
stallion in 2012) and one exposed mare (a domestic 13
year old pregnant Andalusian cross that was bred to the
positive Lusitano by artificial insemination in 2012) were
confirmed CEM positive.
All CEM positive animals were placed under quarantine for
treatment and additional testing. NVSL determined that
the strain of the bacterium from all four positive horses
did not match any T. equigenitalis strains ever found in
the United States, indicating these cases were not related
to any previous cases of CEM diagnosed in the United
States.
The 22 exposed horses were placed under quarantine
until required testing and treatment protocols were
completed.
The 22 exposed horses included:
Eleven exposed stallions from the 2012
breeding season;
Two exposed mares and one exposed foal from
the 2012 breeding season;
Three exposed stallions from 2008;
Four exposed mares from 2008;
One exposed mare from 2007.
1Exposed stallion is defined as any stallion collected at
the stallion station seven days prior to the positive
stallion and seven days after the positive stallion.
2An exposed mare is defined as any mare bred by live
cover or artificial insemination to the positive stallion.
The initial epidemiologic investigation identified 11
exposed stallions and one exposed mare.
Reportable Disease Alert
Contagious Equine Metritis virus is a reportable disease
(pursuant to §9101 of the California FAC, Title 3 California CR
§797 and Title 9 CFR §161.4(f)) and must be reported within
two days of discovery. If your horse is exhibiting clinical signs
consistent with CEM please contact your private practitioner or
CDFA officials.
Reportable Disease List
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